A screw tightening operation occupies a large part of an aircraft assembling process. In the screw tightening operation, plenty of screws to fix various constituent parts of an aircraft are tightened by a preset manual torque wrench as disclosed in, for example, Patent Document 1. The screw tightening operation is generally performed by one combination of an operator and a supervisor.
As described above, a screw tightening operation included in the aircraft assembling process is not performed by only one operator unlike a screw tightening operation included in an automobile assembling process, but is performed by one combination of an operator and a supervisor. The reason will be described below.
Since an automobile has been assembled by an assembly line operation in the automobile assembling process, an area in which an operator performs a screw tightening operation is limited to a small area. For this reason, in the screw tightening operation, an electric torque wrench supposed to be used in a small area is used. The electric torque wrench is held vertically-movably while being suspended from a ceiling, and is supplied with an electric power through a cable to automatically tighten a screw. As a result, even one operator can relatively easily properly perform the screw tightening operation. In contrast to this, in an aircraft assembling process, since it is substantially impossible to assemble a large-scale aircraft by an assembly line operation, the assembling operation is performed at the same place from beginning to end. For this reason, an area in which one operator performs a screw tightening operation is considerably larger than that in an automobile assembling process. Furthermore, an aircraft assembling operation is generally performed at a place having a very high ceiling. Thus, in the aircraft assembling process, an electric torque wrench is difficult to be suspended from a ceiling. Furthermore, when the electric torque wrench is suspended from a ceiling in the aircraft assembling process, since the workable area of the electric torque wrench is limited to a very small area, a screw tightening operation cannot be efficiently performed. For this reason, in an aircraft assembling process having conditions that are totally different from those in an automobile assembling process, a manual torque wrench, the workable area of which is not limited is used, and the same operation is doubly confirmed by one combination of an operator and a supervisor. The double confirmation can prevent undertightening and overtightening a screw and thereby assure the reliability of a screw tightening operation.